FIG. 1 is a side view of a prior art transflective liquid crystal display (LCD) 100 which comprises an LCD panel 110 and a backlight module 120. FIG. 2 is a cross sectional enlarged view of a sub-pixel 200 of the LCD panel 110. The LCD panel 110 comprises a plurality of main pixels for displaying an image. Each of the main pixels is composed of at least three sub-pixels which are red, blue and green sub-pixels. As shown in FIG. 2, the sub-pixel 200 is formed of a first transparent substrate 210, a second transparent substrate 220 opposed to the first substrate 210, and a liquid crystal layer 230 formed between the first and second substrates 210, 220. A color filter layer 240 is formed on the first substrate 210 and comprises a photoresist 242 laid in both a transparent region 204 and a reflective region 202 of the sub-pixel 200. The color filter layer 240 further comprises an opening 244 formed by removing part of the photoresist 242 laid in the reflective region 202 of the sub-pixel 200. On the color filter layer 240 is a flattening overcoat 250. The reflective region 202 of the sub-pixel 200 has a reflective layer 222 formed to reflect light. A thin film transistor switch 224 is formed on the second substrate 220 and is used to generate a potential difference between transparent electrodes 260, 270 so as to rotate the liquid crystals of the liquid crystal layer 230 accordingly and, hence, to control the amount of light passing through the liquid crystal layer 230.
When light is provided by the backlight module 120 to the transflective LCD panel 110 for displaying images, the light will pass through the transparent region 204 of the sub-pixel 200. When light is provided by the environment, such as sun light, the light will be reflected by the reflective layer 222 of the sub-pixel 200. In the prior art, the environmental light can be reflected in two different ways. Suppose the sub-pixel 200 is a red pixel, then light incident along a first path 281 will pass through the color filter layer 240 which will filter out non-red light, thus the reflected light will be red light. Additionally, light incident along a second path 282 will not pass through any color filter layer, thus the reflected light will be generally the same as the environmental light which is generally white light. The same applies to green and blue pixels which will not be described herein.
FIG. 3 is a graph in the CIE coordinate system illustrating the color gamut of the sub-pixel 200 if the sub-pixel 200 is a red pixel. Continue with the aforementioned example, if the environmental light is incident along the first path 281, the reflected light will have a color gamut identified as point A. If the environmental light is incident along the second path 282, the reflected light will have a color gamut identified as point B. The reflective region 202 of the sub-pixel 200 will mix the reflected red light and the reflected white light to generate light with a color gamut on the dash line between point A and point B.
The type and thickness of the photoresist 242 of the color filter layer 242 are determined according to parameters of a specific light source intended for use in the backlight module 120, such as a D65 light source, which generates white light with a color temperature of 6500K, so that the transparent region 204 of the sub-pixel 200 can provide the desired performance. Once the type and thickness of the photoresist 242 have been determined, the photoresist 242 is laid in the reflective region 202 and the transparent region 204. However, after that, the color gamut of the light reflected from the reflective region 202 can only be adjusted by varying the area of the opening 244. Thus the color gamut of the light reflected from the reflective region 202 can only be adjusted to fall on a point of the dash line between point A and Point B in FIG. 3, which often cannot fully satisfy the user's demand. For example, if a calculation result of the overall color gamut including the reflective region 202 and the transparent region 204 indicates that the optimized color gamut of the reflective region 202 should be identified as point C in FIG. 3, then the color gamut of light output from the reflective region 202 can never meet such requirement regardless of how the opening 244 is changed, because point C is not on the dash line between point A and point B.